Introduction
Software-definedstorage(SDS)isadatastoragemethod.Allstorage-relatedcontrolworkisonlyintheexternalsoftwarerelativetothephysicalstoragehardware.Thissoftwareisnotusedasfirmwareinastoragedevice,butonaserveroraspartofanoperatingsystem(OS)orhypervisor.
Software-definedstorageisamajorindustrydevelopmenttrend.Thisindustryalsoincludessoftware-definednetworking(SDN)andsoftware-defineddatacenters(SDDC).SimilartotheSDNsituation,software-definedstoragecanensurethatsystemstorageaccesscanbemanagedmoreflexiblyatanaccuratelevel.Software-definedstorageisabstractedfromhardwarestorage,whichalsomeansthatitcanbecomeasharedpoolthatisnotrestrictedbythephysicalsysteminordertomakethemostefficientuseofresources.Itcanalsobedeployedandprovisionedthroughsoftwareandmanagement,oritcanbefurthersimplifiedthroughpolicy-basedautomatedmanagement.
Difficulty
Theuseofsoftware-definedstorageforlong-termstorageisfullofrisks,suchasdatabiterrors,harddiskfailures,networkattacks,humanerror,andnaturaldisasters.However,inadditiontotheaboverisks,thelong-termstorageofdatamustalsoconsiderotherissues,suchaschangesinhardwarearchitecture,softwareplatforms,applications,anddataformats.
Atthesametime,theincreasingdemandfordataaccessibility,synergy,andbigdataanalysismakestheproblemnotonlyatthestoragetimelimitlevel,butalsoconsideringitsavailability.
Manyenterprisedatacentersareundergoingatransformationfromtraditionalarchitecturetocloudarchitecture.Intheprocessoftransformation,storageisoftenthemostimportantanddifficultpart.Usersneedtousesoftwaredefinitionstounlockvendorlocks,eliminateproprietaryplatforms,andreduceincreasingcomplexity,soastoconvertphysicalstoragedevicesintostorageresourcesforcloudcomputing.Atthesametime,howtorealizetheunifiedmanagementofstorageandthefreeflowofdatabetweentheenterprise'sself-builtdatacenter,outsourcingdatacenteranddifferentcloudserviceprovidersisalsoamajorchallengeintheimplementationofcloudcomputing.
Advantages
Software-definedstorageallowscustomerstointegratestorageservicesintothesoftwarelayeroftheserver.Software-definedstorageextractssoftwarefromtheoriginalstoragecontroller,allowingtheirfunctionstobefurtherdevelopedandnotlimitedtoasingledevice.Comparedwithsoftware-definedstoragethatlimitsdatadeduplicationorthinprovisioningtoasingleharddrive,comparedtoextendingittotheentirestorageplatformlevel,theformerisreallymeaningless.Atthispoint,thepractitionersofsoftware-definedstoragehavenotdraggedeveryonedown.
Oneofthegreatbenefitsofsoftware-definedstorageistostripthesoftwarefunctionfromthearraycontrollersothatitcanbeusedtomanageallthestorageinthedatacenter.
Buttherearestillmanywaystoobtainsoftware-definedstorage.Amongthem,thesoftware-definedstoragedevicemodelthathasreceivedwidespreadattentionrecentlyhasbeenfrequentlyexposed.Anotheradvantageofsoftware-definedstoragedevicesisthatmigrationiseasier.Unlikeothersoftware-definedstorageconfigurations,software-definedstoragedevicesdonotrequiredatatobecopiedtoeachnode,thatis,itdoesnotrequireadditionalstoragespace.Dataisonlystoredinonelocation,andthereisnoneedtocopytheapplicationfromonelocationtoanother.
Butsoftware-defineddevicesareusuallyproprietary,whichiswhatmanyITexpertshopetoavoidintheadoptionofstoragetechnology.
Hiddencosts
However,theindustryrarelymentionsthepotentialhiddencostsrelatedtoSDS.ThehardwaremixingandmatchingthatSDSmaybringwillreversethecostorriskofintegratingsoftwareandhardwaretoendusers.WhenchoosingSDSproducts,itiscriticaltoevaluatewhetherthemanufacturercanprovidethebenefitsofSDS.Timesandtechnologyhavechangedtosomeextent,andsomepeoplesaythatthedrivestandardhasbeenimproved.ButIthinkthatnewhardwaretechnologies,suchassolid-statestorage,areevolvingeveryday.Ifweextendtheabstractionabilityofstoragesoftwaretothemaximum,itshouldbeabletocoordinateanyhardware.IfthisistheidealstateofSDSdeployment,thenthepossibletechnologycombinationsinasystemwillbeunlimited.Underthisassumption,theresponsibilityandcostofverifyingandintegratingnewhardwaretechnologieswillallbeattributedtoIT.
Threechoices
Thefirstchoiceforsoftware-definedstorageistointegratewiththehypervisororexistaspartofitsstack.VMwarehascurrentlydevelopedVirtualSAN,andthecompany'sso-calledsoftware-definedstoragelayerexistsaspartofitssoftwarestack.Hyper-Vhasso-calledclusterstoragespaceandisdirectlyintegratedintoMicrosoft'sHyper-Vstack.
Thesecondsoftware-definedstoragearchitectureincludesthird-party,hypervisor-independentproducts.TheycanworkwithVMware,Hyper-V,KVM,orCitrixproducts.Somesoftwareproductshavecompletefunctions.Itevensurpassesleadingmanufacturersinsomerespects,suchasMaxta,StarwindSoftware,andStoreMagic.Theyprovidethesamefunctionality,butarenotdedicatedtoaparticularhypervisor.Thestoragewarehousestheycreatecanbesharedamongmultipledifferenthypervisors.
Thethirdtypeisvirtualstorage,whichhasbeenaroundforalongtime.ThistypeincludesIBMSpectrumVirtualizeandDataCoreSANsymphonyproducts,whichvirtualizeallhardwareresourcesandabstractthemintoasoftwarelayertoallocateresourcesmoreefficiently.Whenanapplicationloadneedstoconfigurestoragewithaspecificdataprotectionmechanism,youonlyneedtoselecttheconfigurationfromthemanagementinterface,anditwillbeautomaticallyallocatedwiththestorage.
Theconceptofsoftware-definedstorageishuge.Atpresent,manyformsofstorageproductsinthestoragefield,suchasstoragevirtualization,ServerSAN,andhyper-convergedarchitecture(HCI)areallpartofSDS.
1.ControlPlane(controlplane)
AtthelevelofSDSControlPlane,themorefamousonesare:
1)VMwareSPBM(StoragePolicyBase)Management,managementbasedonstoragestrategy);2)OpenStackCinder,CinderisacomponentoftheOpenStackcloudplatformtoprovideblockstorageservices;CindercanaccessmostSANstorageproductsintheindustrythroughaunifiedstoragesoftwareinterface.3)AtypeofstoragemanagementsoftwarerepresentedbyEMCViPR.Thegoalistorealizetheunifiedmanagementofstorageproductsofasinglestoragebrandormultiplestoragebrands,andthepoolingandintegrationofstorageresourcessuchasheterogeneousstoragespace.
2.DataPlane
AttheSDSDataPlanelayer,therearemultiplestorageformsinvolved.
1)BasedonCommodityHardware(basedoncommercialhardware),thispartcontainstwomajorcategories:
HyperConvergedArchitecture(HCI),itshouldbeaServerSANThemorefamoussubsetsare:VMwareVSANorEVO:RAIL,EMCScaleIO,Nutanix,Maxta,etc.
Non-hyper-convergedarchitecture,thatis,anindependentdistributedstoragesystem,themorefamousonesareDELLFluidCache,HPStorVirtual,RedHatInktankCeph,InspurAS13000,etc.
TraditionalSAN/NAS(ExternalStorage),includingSANstorageorNASstorage
Throughacquisitionorself-development,theSDSabstraction(decoupling),pooling,andautomationphasesaregraduallyrealizedTypicalexamplesincludeHPdecouplingLeftHandfromtheoriginalhardwaretoformtheVSAversionofStorVirtual;NetApplaunchedtheVSAversionofONTAPEdgeVSAofDataONTAP;IBMlaunchedtheXIVsoftwareversionofSpectrumAccelerate;DataCoreSANsymphony;EMClaunchedthevirtualizedversionofVNXvVNXWait.
Cloud/ObjectStorage
UseRESTfulAPIandotherinterfacestoinputandoutputdatawithobjectstorage.TherearecurrentlythreeRESTfulAPIs:AmazonS3,SNIACDMIandOpenStackSWIFT.Themorefamousonesare:EMCAtmos,InspurAS13000andsoon.
Constructionprinciples
Software-definedstorage(SDS)technologymayprovideameanstomakestoragemoreflexibleandagile,sovirtualstoragevolumescanbecreatedontheflyandworkwitheaseLoadsareassociatedandmovedorconvertedtogetherwithvirtualmachinesbetweenservers.Inaddition,SDSenablesyoutoassociatevalue-addedserviceswithvirtualstoragevolumes(tonameafew,theseservicesmayincludemirroring,replication,thinprovisioning,anddeduplication/compression),sothatstorageapplicationsareastailor-madeTheneedsoftheworkload.Inaddition,agoodSDStechnologyshouldprovidepathmanagementandinterconnectionloadbalancingtomakebetteruseofphysicalstoragedevicesandserversthateitherhostphysicalworkloadsorvirtualizedclients(orboth)Networkandstructuralconnectionsbetween.
Goal
Thegoalofsoftware-definedstorage(SDS)istoseparatestorageapplicationsfromthephysicaldatastorageinfrastructure.Intheory,thiswillachieve"flexible"allocation,reallocation,andnon-allocationofstorageresources.Inotherwords,SDSprovidesawaytoseparatestorageservicesfromstoragepackages.Evenifthebasichardwareandinterconnectionarechanged,itcanstillprovidevolumecontinuity.
Thiscapabilityisespeciallysuitableforapplicationsthatareextractedfromserverhardwareor"virtualized"andcanbemovedbetweenservers,networks,orstoragestacks.
ByusingSDS,forphysicalresources,thestoragevolumepresentedtoavirtualizedworkloadoraclientisitselfanabstractionlayer,ratherthanaphysicalconnection.ThisSDSvolumecanbemovedbetweenhoststogetherwiththeworkload,providinganewpathwiththesameonlinestorageresourcesthroughtheSDSservice.Therefore,itisnotnecessarytocopythedataofeverypossiblehost.